Contact connection for wire-shaped heating elements



s p 25, 1967 G. c. LE GARGASSON ETAL Filed Feb. 26, 1965- FIG? INVENTOR.GEORGES C.LE GARGASSON MAROEL J. CADIOU AGENT United States PatentClaims. (cl. sss-274 ABSTRACT OF THE DISCLOSURE A contact connectionbetween a conductor surrounded and insulated from a metallic envelopeand a metallic pin. The end of the conductor is stripped of itsinsulation and surrounding envelope and secured to the pin. A ceramicsleeve surrounds the exposed end of the conductor and is hermeticallysealed at its ends to the envelope surrounding the conductor and themetallic pin.

This invention relates to a contact connection between a wire-shapedheating element comprising one or more electrical conductorselectrically insulated 'by a powdered metal oxide and enclosed in ametallic envelope, and a plurality of associated connecting pins whichare thick relative to the conductors, the ends of the conductorsstripped of their insulation and envelope being soldered to theconnecting pins and the envelope and the pins being surrounded by anelectrically insulating mass through part of their length. Such aconnection is known.

The known contact connection uses glass as the insulating mass, thuspreventing ambient moisture from penetrating the powdered oxide betweenthe envelope and the electrical conductor since absorption of moistureby the oxide would cause a considerable decrease in breakdown voltagebetween the conductor and the envelope.

The use of glass as the electrically insulating material in a contactconnection has the disadvantage that the connection is not veryresistant to mechanical oscillations or shocks. Further this connectionis usable only up to an operating temperature which is lower than thecomparatively low softening point of the glass employed.

An object of the invention is to provide a gasand water-tight contactconnection which is very strong, which permits a high current strengthand which is suitable to withstand high operating temperatures of manyhundreds of degrees centigrade.

The contact connection according to the invention is characterized inthat the electrically insulating mass is in the form of a sleevesoldered at its peripheral edges to the envelope and the pins in agas-tight manner, the sleeve being of a ceramic material such as, forexample, aluminum oxide over at least that portion which surrounds thearea where the conductors emerge from their envelope. Preferablysintered ceramic material is used as the electrical insulating material.

By suitable choice of its density, the sintered ceramic material ispermeable to light. This affords the attractive possibility forinspecting the connection visually during operation. It is then possibleto ascertain whether the temperature of the conductors emerging from theenvelope of the element becomes excessive. If the temperature becomesunduly high at this area and if the conductors commence to show, forexample, red incandescence, this can be observed because of thetransparency of the ceramic material. In this case steps may be taken toreduce the temperature, for example, by external cooling with air orwater.

The sleeve of ceramic material must be soldered at "ice its peripheraledges to the metal envelope of the element and the connecting pins in agas-tight manner. To this end, the sleeve of ceramic material could belocally metallized to permit working with copper-silver solder. Suchmetallizing is an expensive operation. In another embodiment of theconnection according to the invention it is preferred to use atitanium-containing eutectic of silver and copper as the solderingmaterial.

It has been found that in a connection established between a ceramicmaterial and the envelope of the heating element by using a soldercontaining titanium, the titanium diffuses into the material of theenvelope rendering it brittle. An embodiment is therefore preferred inwhich the sleeve is not made wholly of ceramic material but comprisestwo portions, that is to say a metallic first portion soldered to theenvelope and a ceramic second portion soldered to both the connectingpins and the first portion. For the attachment of the first portion itsulfices to use, for example, a copper-silver soldered connection, thetitanium-solder being used, as before, for the two operations ofsoldering to the second portion.

The invention will now be described with reference to the accompanyingdrawing, in which:

FIGURE 1 shows in cross-section one'embodiment of a contact connectionbetween a coaxial heating cable and a connecting pin, which is in theform of a plug socket;

FIGURE 2 shows in cross-section another example of a contact connectionbetween a heating cable having two current conductors and two connectingpins.

The wire-shaped heating element of FIGURE 1 comprises a metallicenvelope 1 and a central electrical conductor 2 which is insulated fromthe envelope 1 by a powdered metal oxide 3. The conductor 2 is strippedof insulation at its end 4 and extends into a bore formed in a terminalportion 15 of a connecting pin 7 having the form of a plug socket. Theenvelope '1 and the terminal portion 15 are surrounded by a sleeve 6 ofa sintered ceramic material having a density such as to belight-transmitting. The numeral 5 indicates a metal sleeve. All theconnections in this example are soldered. A ring 8 likewise of ceramicmaterial is oriented within the envelope 1 over part of its length.

The connection of FIGURE 1, in which the parts to be joined have beenpreviously degreased carefully with the aid of a suitable liquid, wasmade as follows:

First a ring of soldering material, an eutectic of copper and silver,was placed on the envelope 1 at the area indicated by 11. (The positionafter soldering is shown.) Then the sleeve '5, which has a coefficientof expansion approximately equal to that of the sleeve 6, was slippedover the envelope '1. The sleeve 5 is made of an ironnickel compoundcontaining 42% of nickel and the sleeve 6 is of sintered aluminum oxide.A ring consisting of solder of a titanium-containing eutectic of copperand silver was then placed in position at 12. Next the sleeve 6 and aring of solder were arranged at 13, the envelope 1 being displaced so asto project slightly from the sleeve '6. Then the ring 8 of sinteredaluminum oxide and a ring of a solder having a very high melting pointwere fitted at 14, the rings s and 14 contacting each other. This ring14 is of an alloy consisting of 85% of silver and of manganese andhaving a melting temper-' ature of 950 C. The connecting pin 7, which isof iron nickel (42% of nickel), was then slid with its terminal portion15 into the sleeve 6, causing the envelope 1 to be pushed back into thesleeves 5 and 6. The terminal portion 15 has a diameter such that, onthe one hand, the heat within the conductor portion 4 deprived ofinsulation and surrounded by the ceramic sleeve 6 can be dissipated and,on the other hand, the heat produced in the terminal portion 15 due tothe passage of current is negligible.

The whole was then introduced into an oven in which an atmosphere ofhydrogen was maintained. Any trace of oxygen and water vapor wasavoided. The temperature of the oven was approximately 1,000 C. Afterheating the connection for a period which depends on the diameter of theheating element and the dimensions of the contact connection, theconnection was cooled while retaining the atmosphere of hydrogen in theoven.

The dimensions and the electrical properties of a contact constructionmanufactured in accordance with FIG- URE 1 are the following:

Millimeters Diameter of the envelope 1 2 Length a of the sleeve 5 7Length b of the sleeve 6 7 Length c of the pin 7 18.5 Length of theterminal portion 5 Diameter of the terminal portion 15 2 length overwhich the end 4 extends into the terminal portion 5 is approximately 1cm.

It has been found that a connection of the kind herein described to aheating element having a central current conductor of nickel-chromium0.7 mm. in diameter, when exposed to air, can withstand an intensity of30 amps. for several days and even 40 amps. have been measured in thistest for a short period. The gasand water-tightness of the constructionwas found to be perfect. During the tests a cool flow of air wasmaintained at the sleeve 6. Even higher current strengths arepermissible if a very cold gas (air, nitrogen CO is blown against thesleeve 6 or upon immersion in running water. The latter suggestion canbe carried out because of the high gas and water-tightness of theconstruction.

In the embodiment shown in FIGURE 2, the heating element comprises twoelectrical conductors which are secured at their ends 3'6, 3'7 strippedof their insulation in bores of nickel coupling pieces 25 and 27 in themanner shown. The two coupling pieces are insulated electrically fromeach other by a ceramic plate 32 and have further bores to receiveiron-nickel connecting pins 26 and 28. Further more ceramic rings 24 and31 are provided. The two connecting pins 26 and 28 are maintained inposition by a sleeve 29 of sintered ceramic material.

The various parts, which have previously been degreased, were assembledas follows:

A sleeve 23 consisting of a nickel-iron compound with 42% of nickel wasslipped over an envelope 33 of the heating element, a ring of solderingmaterial (an eutectic copper-silver compound) being arranged at 38. Bymeans of this ring the sleeve 23 could be soldered to the envelope 33 ofthe heating element throughout its length. Then a ring 31 consisting ofsintered aluminum oxide and having two apertures was slipped over theends 36 and 37 of the heating wires whereupon a ring 24 was broughtaround the heating 'wire and the two coupling pieces 25 and 27 wereslipped over the ends 36 and 37 in the manner shown. A plate 32 ofsintered aluminum oxide was arranged between the coupling pieces 25 and27 to avoid any contact between them. Next, rings of a silver-manganesesolder were arranged at 40 and 41.

The assembly thus obtained was introduced into an oven in which anatmosphere of hydrogen at 1000 C. was maintained similarly as in theprevious example.

After cooling had taken place while retaining the atmosphere ofhydrogen, the assembly was removed from the oven and the sleeve 29 ofsintered aluminum oxide was slipped over the rod-shaped part 26 and 28,whereafter rings of a titanium-containing eutectic copper-silver solderwere arranged at 43, 44 and 45. Then another soldering operation wascarried out in the oven and the sleeve 29 attached.

Under similar conditions to those in the first example described withreference to FIGURE 1, a contact connection established as shown inFIGURE 2 in a heating element two mms. in diameter and with two heatingwires, each of 0.36 mm. in diameter was found satisfactorily towithstand a current strength of 15 amps. without undue heating or anyattack of the tightness of the connection being noticeable.

The dimensions of the various parts of this connection are thefollowing:

Length (1 of the sleeve 23 mm 5 External diameter of the sleeve 23 cm 1Length e of the sleeve 24 mm 2.5 Diameter of the sleeve 24 'mm 6 Lengthf of the sleeve 29 cm 1 External diameter mm from 8 to 9 What is claimedis:

'1. A connector for a heating element having at least two conductorssurrounded by a common metal envelope, said conductors being insulatedfrom. one another and from the envelope, the ends of said conductorsbeing stripped of insulation, a ceramic member having parallel boresthrough which connecting pins for each of said conductors extend,metallic coupling members surrounding and secured to each of saidconnecting pins, each of said coupling members having a bore throughwhich the end of the conductor extends and is secured thereto, a metalsleeve surrounding and hermetically sealed at its peripheral edges to aportion of the metal envelope, said ceramic member surrounding a portionof said conductors intermediate each of said coupling members and themetal sleeve and being hermetically secured at its peripheral edges tosaid metal sleeve and said connecting pins.

2. A connector as claimed in claim 1 in which the ceramic membersurrounding the conductors is of lighttransmitting sintered ceramicmaterial.

3. A connector as claimed in claim .2 in which the ceramic material isalumina.

4. A connector as claimed in claim 3 in which the ceramic member issealed to the metal sleeve with a titanium containing eutectic of silverand copper.

5. A connector as claimed in claim 4 in which the coupling members areseparated by a ceramic member.

References Cited UNITED STATES PATENTS 1,901,667 6/ 1933 'Roh 174--11.3

FOREIGN PATENTS 1,123,417 2/ 1962; Germany.

99,812. 4/ 1962 Norway.

OTHER REFERENCES Jenny, A. L., Soldered Ceramic-to-Metal Seals, ProductEngineering, December 1947, pp. 154-157.

RICHARD M. WO'OD, Primary Examiner.

J. G. SMITH, Assistant Examiner.

1. A CONNECTOR FOR A HEATING ELEMENT HAVING AT LEAST TWO CONDUCTORSSURROUNDED BY A COMMON METAL ENVELOPE, SAID CONDUCTORS BEING INSULATEDFROM ONE ANOTHER AND FROM THE ENVELOPE, THE ENDS OF SAID CONDUCTORSBEING STRIPPED OF INSULATION, A CERAMIC MEMBER HAVING PARALLEL BORESTHROUGH WHICH CONNECTING PINS FOR EACH OF SAID CONDUCTORS EXTEND,METALLIC COUPLING MEMBERS SURROUNDING AND SECURED TO EACH OF SAIDCONNECTING PINS, EACH OF SAID COUPLING MEMBERS HAVING A BORE THROUGHWHICH THE END OF THE CONDUCTOR EXTENDS AND IS SECURED THERETO, A METALSLEEVE SURROUNDING AND HERMETICALLY SEALED AT ITS PERIPHERAL EDGES TO APORTION OF THE METAL ENVELOPE, SAID CERAMIC MEMBER SURROUNDING A PORTIONOF SAID CONDUCTORS INTERMEDIATE EACH OF SAID COUPLING MEMBERS AND THEMETAL SLEEVE AND BEING HERMETICALLY SECURED AT ITS PERIPHERAL EDGES TOSAID METAL SLEEVE AND SAID CONNECTING PINS.